US air safety officials are investigating a Boeing 737-800 plane that was missing a panel when the United Airlines flight landed on Friday.

The Federal Aviation Authority is probing United Airlines Flight 433, which left San Francisco and landed in Oregon on Friday. It was carrying 139 passengers and six crew members.

Amber Judd, director at Rogue Valley International Medford Airport, said the plane landed safely and the external panel was discovered missing during a post-flight inspection.

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The airport paused operations to check the runway and airfield for debris but none was found.

A United Airlines spokesperson said no emergency was declared because there was no indication of the damage during the flight.

“We’ll conduct a thorough examination of the plane and perform all the needed repairs before it returns to service,” the spokesperson said.

“We’ll also conduct an investigation to better understand how this damage occurred.”

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The missing panel was on the underside of the aircraft where the wing meets the body and just next to the landing gear.

The plane in question made its first flight in April 1998 and United Airlines has operated it since November 2011.

It is a 737-824 plane, part of the 737-800 series that was a precursor to the MAX.

Boeing did not comment, and instead directed questions to United Airlines.

Friday’s incident is the latest in a series of problems for Boeing, which has resulted in investigations into the company’s safety and quality standards in its production process.

In January, a panel that plugged a space left for an extra emergency door blew off a Boeing MAX 9 jet in mid-air just minutes after take-off, leaving a gaping hole and forcing pilots to make an emergency landing. There were no serious injuries.

The US Department of Justice has launched a criminal investigation.

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Alaska Airlines Flight 1282 Boeing 737-9 MAX was forced to make an emergency landing with a hole in its fuselage. Pic: Reuters.
Image:
Alaska Airlines Flight 1282 Boeing 737-9 MAX was forced to make an emergency landing in January with a hole in its fuselage. Pic: Reuters.

On 6 March, fumes detected in the cabin of a Boeing 737-800 Alaska Airlines flight destined for Phoenix forced pilots to head back to Portland airport.

Seven people, including passengers and crew, requested medical evaluations but no one was taken to hospital, officials said.

At least 50 people were injured on Monday after a Boeing 787-9 Dreamliner flying from Australia to New Zealand suddenly dropped without warning – with people who were not wearing seatbelts tossed from their seats and flung into the cabin ceiling and aisles.

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Moment plane loses tyre during take-off

Last week, a United Airlines-operated Boeing 737 MAX rolled on to the grass and off the runway in Houston while another United-operated Boeing bound for Japan lost a tyre after take-off from San Francisco and was diverted to Los Angeles where it landed safely.